Share-Based Compensation Arrangements (Share Options Activity) (Details) (Share Options [Member], USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Share Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Options Outstanding	685,937		712,061
Share Options Outstanding Weighted Average Exercise Price	$ 23.39		$ 22.96
Share Options Granted	106,775	57,450
Share Options Granted Weighted Average Exercise Price	$ 23.37
Share Options Exercised	(113,324)
Share Options Exercised Weighted Average Exercise Price	$ 20.08
Share Options Forfeited or Expired	(19,575)
Share Options Forfeited or Expired Weighted Average Exercise Price	$ 26.79
Share Options Outstanding Weighted Average Remaining Contractual Term	5
Share Options Outstanding Aggregate Intrinsic Value	$ 2,267
Share Options Exercisable	427,912
Share Options Exercisable Weighted Average Exercise Price	$ 24.89
Share Options Exercisable Weighted Average Remaining Contractual Term	2.8
Share Options Exercisable Aggregate Intrinsic Value	882
Share Options Expected to Vest	258,025
Share Options Expected to Vest Weighted Average Exercise Price	$ 20.90
Share Options Expected to Vest Weighted Average Remaining Contractual Term	8.7
Share Options Expected to Vest Aggregate Intrinsic Value	$ 1,385

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The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of vested portions of options outstanding and currently exercisable under the option plan as of the balance sheet date.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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The weighted average period between the balance sheet date and expiration for all vested portions of options outstanding and currently exercisable (or convertible) under the plan, which may be expressed in a decimal value for number of years.

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The weighted average price at which option holders acquired shares when converting their stock options into shares under the plan during the reporting period.

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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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The combined weighted average exercise price associated with stock options during the period that have either lapsed or been forfeited.

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Net number of share options (or share units) granted during the period.

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The weighted average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on stock options awarded under the plan during the reporting period.

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The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices pertaining to options outstanding under the plan as of the balance sheet date.

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The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including vested options.

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The weighted average price as of the beginning of the year at which grantees can acquire the shares reserved for issuance under the stock option plan.

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The weighted average period between the balance sheet date and expiration for all awards outstanding under the plan, which may be expressed in a decimal value for number of years.

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As of the balance sheet date, the total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of fully vested and expected to vest options outstanding.

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As of the balance sheet date, the number of shares into which fully vested and expected to vest stock options outstanding can be converted under the option plan.

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As of the balance sheet date, the weighted-average exercise price for outstanding stock options that are fully vested or expected to vest.

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The weighted-average period between the balance sheet date and expiration date for fully vested and expected to vest options outstanding, which may be expressed in a decimal value for number of years.

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Number of share options (or share units) exercised during the current period.

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